Precaution number 1: Don't do it inside your home! If you "have to" keep it in an isolated room with a fire alarm, and the windows ajar for good ventilation in case of any vapours. But dont make a habit of it.
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ppumkinFeb 10 '12 at 9:10

Why? Is the battery dead and he wants to charge it 1 time? Or does he leave his car idle for months at a time and he wants to keep the battery topped off?
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Jay BazuziFeb 15 '12 at 17:54

@Jay Bazuzi: In this scenario the battery is suddenly dead because of very cold weather and the car being driven for not enough miles to recharge it.
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sharptoothFeb 16 '12 at 7:03

4 Answers
4

A battery represents a heavy mass of chemical and electrical energy. It should be treated as a fairly dangerous object if it makes its way into your home. Some of the risk factors include:

Heavy: a car battery is a heavy object. Ensure that it is in a stable location with no change of tipping or falling because it is full of ...

Acid: a car battery is full of sulphuric acid. Ensure that is has no chance of tipping, spilling or otherwise expelling acid onto people, pets, valuables or even many metals. Remember, you are about to make the situation even worse by introducing ...

Electricity: be very careful with the terminals of a car battery. There are plenty of amps in there waiting to jump into a conductor and make enormously exciting and dangerous sparks. Keep in mind that when charging a car battery, it will produce hydrogen gas of some concentration. Ensure that the environment is well ventilated because otherwise there's an excellent chance of a dangerous ...

Fire: have a fire extinguisher in your hand. Note: you will have to make a judgment call on what type you need: what will the hydrogen ignite and how will you put it out? Where will the acid go when you start hosing it around with the extinguisher?

If I were forced to do this inside my house, I would put the battery in a large Pyrex casserole dish on the floor, run the charger from a GFCI outlet (to act as an additional ciruit breaker) and keep the fire extinguisher in my hand.

I would also wait until my wife was not home and I would not tell her later about the dumb thing I did today....

In all seriousness, what I would do (and have done) is to connect the battery charger to the battery while it's still in the car. Then I would plug the charger into an extension cord (or series thereof) until such time as I could reach a plug with main power. The risks of a car battery inside the house are significant and the benefits (convenience? hardly!) are small enough that they're difficult to measure.

What about those new batteries that are completely sealed? Do those still release hydrogen vapors? If so, where do those vapors come out from exactly?
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GetFreeJan 22 at 22:13

@GetFree, check the wikipedia entry on sealed lead acid batteries. That valve for gas blow-off? That's where the hydrogen comes out. There's nothing to be done there, that's just how chemistry works.
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Bob Cross♦Jan 22 at 23:24

Thanks. What about those jump starters like this one? Those have a lead-acid battery inside and are meant to be charged indoors. Are the hydrogen vapors a problem in that case?
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GetFreeJan 22 at 23:47

@GetFree, I think you need to read the MSDS a little more closely.
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Bob Cross♦Jan 23 at 1:56

I have been working in the power industry for 15 years as an operations engineer. Power stations require DC (battery) power as a secondary / back up power source should the AC (mains / system power) supply develop a fault resulting in loss of primary power hence all power stations have battery banks to supply critical motors & control systems to safely shutdown the plant & then address the fault. The point: the battery banks are considered a major hazard in the industry, classified as hazardous areas with restricted access requiring atmosphere monitoring, batteries release hydrogen when charging, for that reason the batteries are housed in a separate enclosure with forced ventilation (ventilation fans), granted we are talking a much larger scale, but the batteries used are batteries you will find in lorries or similar just lots of them, the size of the enclosure & ventilation flow is all relative, ie the enclosure is large & fans capable of displacing vast amounts of air, so a small battery in a small enclosure with no ventilation presents a similar sort of hazard. The fans have redundancy built in, meaning 2 fans (1 duty, 1 standby) further demonstrating the significance of the hazard batteries present often the vent fan running signal is fed back to the control system & alerts the control room staff of failure, this also cuts out the battery charger. Ie the batteries will not charge if no vent fan running. Charging batteries in a cupboard with no ventilation in your home is far from ideal, hydrogen is the most volatile of gases (explosive range is 5%-75% volume in air) meaning any significant release of hydrogen is almost certainly going to become an explosive mix of fuel/ air. Charging a large volume of batteries in a home coupled with the number of ignition sources in a house is asking for trouble, a hydrogen explosion is quite something, do a quick web search on hydrogen explosions, it may sway your choice of charging options. A saying in our industry is 'routine wrong' it relates to things we know & do that are wrong but haven't had an incident, just because nothing has happened in the past it doesn't guarantee it won't happen in the future, luck is often the reason incidents have not occurred or on the flip side of the coin bad luck & poor judgement is the reason incidents occur. Whichever nearly all incidents are avoidable, why take the chance, My advice is take heed of the comments leaving the battery in the car, if like the gentlemen in Wisconsin the ambient temperature isn't conducive to charging a battery follow the advice on the other comments, most importantly charge in well ventilated area.

All 4 are plugged into a battery tender and are on the bottom rack of a little cabinet thing my wife got at Target with a towel underneath to avoid any drips from the non sealed battery.

On the top rack there is 2 Ryobi 18V chargers and 2 Sears 12V chargers for all my tools as well as as another 18V charger for a hoover lynx and another charger for a battery jump starter.

With the doors open on this cabinet at night it looks like a UFO landing between all the different colors of the charger lights.

I believe this setup is perfectly safe and it is all plugged into a Surge Strip which goes out the back into a GFIC outlet.

The reason I have them all in the house is because of the weather. Here in Wisconsin batteries dont really like to charge to well in 0 degrees. While I am aware batteries should be stored in a cool place my mud room laundry room doesnt have a vent in it and is off the kitchen so it is always about 65 degrees. If I leave for the weekend or something I just turn the surge strip off and have no worries.

There are so many reasons not to charge a car's starter battery in a living space:

battery acid on your clothes when you carry it

hydrogen buildup that could explode

you're going to use an all-metal wrench to remove the battery cables, which makes it easily to accidentally create a short circuit on a device designed to dump a lot of amps quickly

The easiest way to deal with this problem is to jump-start the car and then drive to recharge the battery. You don't have to remove the battery, or risk hydrogen buildup indoors, or get battery acid on your clothes.

Your deeply-drained starter battery is probably sulfated now. It won't be able to hold as much charge, and so won't be able to put out as much cranking current. It's worse when it's cold, so you may find it won't start again the next really cold morning.

Take it to an auto parts place once it's fully charged and they'll test it. The result will be in CCA (cold cranking amps). They can advise you whether you should replace the battery.

There are several different types of chargers out there. Some are pretty dumb, sending a fixed voltage to battery over time. That will do the job of charging up a dead battery, but if you leave it on the charger too long, it can boil the battery fluid. Some even have the ability to supply a lot of amps, so they can be used to jump-start a car if you don't have another car handy.

Smarter chargers have a circuit that moderates the output over time, to bulk-charge the first 80%, and then gently bring it up to full charge, which is something lead-acid batteries like.

Even smarter chargers have a program to de-sulfate a battery, although it takes a long time. Your car would be out of commission in the meantime.

To keep batteries topped off, a smart trickle charger like the Battery Tender is a good choice. I like these for vehicles that side idle a lot of the time.